Question

Problem #10: (20 points) 7. A student separated the pigments from spinach extract using column chromatography. The B-carotene fraction was 10 mL, but when the student measured the absorption at 455 nm, it was greater than one so the student decided to dilute the sample. The sample was diluted by taking 1 mL of the B-carotene fraction and diluting it to a total of 5 mL using the solvent mixture of 10% acetone / 90% hexanes. The absorption of this diluted sample was measured to be 0.5 at 455 nm. A lcm cuvette was used for all absorption measurements. Compound B-carotene max 455 nm &M'cm') 1.35 x 105 (a) What is the concentration of B-carotene in the diluted sample? (b) What is the concentration of B-carotene in the original sample collected from the column? (c) How many moles of B-carotene were collected from the column? (d) By changing the running solvent to a mixture of 15% Acetone / 85% Hexanes, what do you expect to happen to the Rf value? Would the column run faster or slower?

Please show any work that you can!!

This is all the info that is given, What info is missing??

Answer 1

au & = 1.35x105 Mann max= 455 nm. A 0.5 b= l an. using beer's low Aeb.c A absorbane & molers absorptivity b. path length Comoher concentration C: E.D C : 0.5 1.35x105 XI = 3.7 X10 CM. diluted sample contains s.7810 MB. Carotene (6 Vi X Ci = vfx Cf . (C) Na volume C Concentration Vi= 1 me vf = 5 me, cf = 3.78100 M. ci- vf xf . sud x 9.7x100 M Vi lut = 1.852x10-5M Concentration of s. Carotene in original sample= 1.852810 M Molar Mass of ß-carotene - 536.873 g/mole. concentration of B-Carotene collected from column = 1.852x105 mole/ some or o.soll solution ar extracts contains bß-Carotene - 0.rolar) x 1.852x10 mole/x = 1.85810-7 mole. 1.85x10 moles ß-Carotene onre were collected from column. I .

(d) beta- carotene is a non-polar organic compound which is highly soluble in a non-polar solvent like benzene, hexane etc. During the extraction and purification of beta- carotene, the column runs faster when increased non-polar percentage in the solvent mixture as this compound is more soluble in a non-polar solvent.   In this case, when the solvent of mixture of 15% acetone and 85% hexane is applied through the column it runs slower and Rf value decreases compare to the solvent used of 10% acetone and 90% hexane.